Electric heating device



March 19, 1929. E, MEGANE, 1,706,016

ELECTRIC HEATING DEVICE Filed Aug. 24, 1925 2 Sheets-Sheet 1 lllallalalrflllalaa idw/'n L Wiegand March 19, 1929. E. WIEGAND 1,706,016

ELECTRIC HEATING DEVICE Filed Aug. 24, 1925 2 Sheets-Sheet 2 f'dwx'n L IX//sgand Attorney;

Patented Mar. 19, 1929.

UNITED STATES PATENT OFFICE.

EDWIN L. WIEGAND, or DoRMoNT, PENNsYLvANIA, AssIGNoR 'ro EDWIN n WIE- GAND COMPANY, oP PITTSBURGH, PENNSYLVANIA, A coRPoRAfrroN or PnNNsYL VANIA..

ELEC'JRIC HlElATllINGv DEVICE.

Appucatmn mea August 24, 1925. serial No. 51,982.

Thisinvention relates to' electric heating devices and has special reference to the use l of metal sheathed heating units of the type set forth in my prior applications Serial Nos.

660,294, and 697,446, tiled respectively August 31, 1923-,Y and March 7 1924.

VThese 'units .are characterized by having a cementitious mass which is a non-conducto;`

of electricity embracing a resistance element and in turn embraced by a sheet metal shell which serves to protect thecementitious mate-l rial from becoming disintegrated by mois-r ture or atmospheric influence or impregnated with grease or other decomposable and electrical conducting substances or becoming mechanically disintegrated and also serves to conduct heat mechanically to any cooking utensil or other vessel placed thereon. Such heating units can be made of very Ihigh energy density owing to the efficient mannerin which they conduct heat from the re- -sistance wire and they suffer no deterioration incase they be used in connection with a heat conducting body capable of removing the heat as rapidly as generated 4and so preventing the temperature from rising to a .dangerous degree. On the other hand any unit of this character is obviously subject to early destruction in case the eurrentbe supplied without at thesame time supplying some path of escape. for the heat generated. In all such devices it is necessary, for eco- 'nomy in operation, to insulate the heat units as thoroughly as possible in order to prevent loss of heat excepting to the article whichl is to be heated, but this desirability obtains only until the desired operating temperature is reached and at higher temperatures it becomes desirable to provide a leakage path or spillway so that the excessive heat may be dissipated. A steam boiler offers an analogous example wherein waste of steam pressure is avoided until working pressure is' attained after which a-safety v'alve.is employed to release the excessive pressure` which arises if the ire is continued after the engine .is stopped.

The objects of the present invention are the provision of supporting means for heating units of this type which shall, at least in great measure, serve as safety valves for the `clad4units which may be made of diii'erent materials according to the demands or prejudices of different users which shallconserve heat at low temperatures and dissipate the same at high temperatures.

. My inventive idea may be embodied in numerous physical forms, a few of whichV are illustrated` in the drawings accompanying and forming a part of this application. Fig. l illustrates a preferred form of the in vention arranged to be used in connection with an ordinary stove top; Fig. 2 is an enlarged detail view of a part of the device shown in Fig. 1; Fig. 3 is a detail view corresponding to the line 3-3 of Fig.l 2; Fig.- 4 is a similar view showing a modified form of unit; Fig. 5 is a sectional view ofla modified form of support Fig. 6 is a sectional view showing another modilication; Fig. y7 is va sectional view of amodification showing the use of a unit of diiierent shape; Figs. 8 and 9 are sectional views showing modified forms; Fig. 10 is a plan view of apart of the device shown in Fig. 7, the element being omitted; Fig. 11 is a plan ,view of a part of the device shown in Fig. 9, 'one end of the unit being omitted; Fig. 12 is a sectional view ot another modiiication; Fig. 13 is a top plan view oia part of the device shown in Fig. 1.2; and Fig. 14 is a top plan view of the de vice shown in Fig. 6 with the heating elements omitted. a

The unit for which my improved supportmg device is primarily designed consists of a hollow sheet metal shell made in two parts 1 and 2 suitably spun or otherwise fastened together at 3 and packed full of a suitable cementitious material 4in which is embedded one or more resistance elements 5 arranged in accordance with any desired pattern. In case the device is made for high voltages each resistor is preferably made of comparatively smallwire Wound into a helix as shown in i Figs. 2 and 3, care being taken that the turns be not so close together as to prevent this cementitious material from filling the interior of the same at all points, and the resulting coil is laid in the cement according to any desired pattern, preferably being looped in sinuous form so as to heat all parts uniformly. In case a multiple heat unit is desired, multiple resistors are employed, being intertwined together in such manner as will heat all parts, one arrangement being shown in Fig. 3. Some of the units, however, are made with other forms of resistors such as the plain wire 46 shown in Fig. 4 which may be either round or flat as desired, and looped back and forth Without coiling. Sometimes these units are made in the form of complete annuli, sometimes in the form of incomplete annuli, sometimes in the form of short arc` uate sections, and sometimes in the form of straight bars, all of these forms being lset forth in my different applications hereinbefore identified. I have shown here complete annuli in Figs. 1 and 6 and incomplete strips are here shown as fiat on their working faces, being intended for use with fiat bottom vessels, but it is included in my invention to make them dishing to receive a round bottom vessel or other special shape; and they are preferably made rather thin with parallel faces although I do not limit myself in this regard.

In the form of the invention shown in Fig. 1 I have illustrated two annular units of unequal size located concentrically, one within the other, with their working faces substantially in the same plane, these units being laid in grooves 10-10 in a cast metal plate 11. The top surface'of this plate is formed between the grooves with a narrow rib 12 and also inside the inner groove with a circular boss 13 and outside the outer groove with a circular rim 14. The outer margin of the plate is rabbeted as shown at 15 to fit the rim of a sheet metal basin 16 whose brim 17 extends outwardly and is turned downwardly as at 18 to fit the customary hole in a stove top 19. This basin is here shown as having a bott-om 2O provided at one point with aterminal support 21 equipped with suitable binding posts 22 suitably connected to the units; and overlying this bottom and partly filling the basin I have shown a layer 23 of heat insulating substance such askieselguhr, magnesis, etc.

The bottom of each of the grooves 10 is formed with projections, irregularities, or other spacing means illustrated in Fig. 2 as inte ral teeth 24 on which the unit rests. Pre erably these are made in the form of sharp ledged annular ribs, machined in the metal and exhibiting clean and metallic faces between the ridge, but this is unduly expensive for ordinaryv use and the requirements of my invention are met by casting the ribs directly, or by making same as discontinuous projections arranged according to any desired pattern, or by providing spacing devices of other substances such as isolated nodules of sand cast in the metal. When Sand is used, however, itis desirable that the same be not used in a continuous layer since it has too great an insulating effect; and in any case it is desirable that the projections or lspacing devices be rigid with the plate else the user considers them as accidental and deleterious and removes them with consequent injury to the behavior of the device.

The operation of the device is as follows: The metallic contact between the unit and support is very small and when a cooking vessel or other utensil is in place upon the unit (which preferably projects slightly above the top of the plate) only a small proportion of the heat generated escapes into the supporting plate. Even in the absence of any heat absor ing utensil, the rateof increase of temperature of the units is far greater than that of the support owing to the fact that conduction is limited and radiation is very low at low temperatures, but as soon as the temperature of the unit rises to a dangerous point, the radiation loss to the plate increases very rapidly, owing to the small height of the projections which is preferably only about one hundredth of an inch with the result that the com aratively large heat dissi- 4pating surface of the supporting plate becomes available.

In Fig. 5 I have shown a non-metallic supporting plate containing my improvements. Owing to the fact that the luminous wire heating units have long been mounted in grooves in round porcelain disks many conservative manufacturers and users desire to continue to use this material. Porcelain is well known to be a very poor conductor of electricity, but I consider it a rather good conductor of heat and yfor purposes of this application I describe it as a heat conducting material. One form of my invention employing such a porcelain plate is shown in Fic'. 5, the plate 30 being circular and provided with a wide, fiat, annular groove 31 receiving the annular, metal-sheathed, heating unit 32. The bottom of the groove is formed with teeth or ribs 33 providing a considerable number of small points of support for the unit so that heat conduction therefrom is limited, although radiation from the unit is readily absorbedas soon as the radiating temperature is attained. A substantial advantage of porcelain in this connection is in addition to being a rather good conductor of heat it is an excellent absorber of heat radiation.

In Figs. 6 and 14 I have shown another arrangement wherein 35 denotes a circular porcelain disk having therein a circular recess 36 whose bottom exhibits a series of intersecting ribs 37 on which the metal-clad heating unit is supported. When an annular unit is employed it is' desirable to close its central aperture as by a hollow metal clad,"elements ll0--4i0 laid in paralle'lgroovesI Lil'in a rectangular ceramic tile 42, the bottom of each groove having ribs or projections 43 therein upon which the units rest for the purposes heretofore explained.

In Fig. 8 I have shown a circular plate 50 having a groove 51 receiving the unit 52, the

bottom of the groove having a smaller groove 53 in which is laid the metal ring 54 Whose top. face is preferably located somewhat belovvs7 and out of contactfwith the unit. It is often times sufficient merel to form this groove 51 in the bottom of t e main groove without providing any outside avenue of escape for the heat, although it is often advantageous to form the bottom of the unit -recess with radial channels as shown in Figs.

9, 11, 12 and 13 wherein the groove 51 has its bottom traversed by a series of closely adjacent radial channels 55 defining a plurality of radial supporting ribs 56. These ribs may either be plain as shown in Figs. 9 and l() or may be intersected bythe circumferential groove 53;'and the same may either be extended 'beyond the margins of the unit so as to define openings 57 communicating with the outer air as shown in FiUs. 9 and 11, or they may terminate at the wallns of the main groove as shown in Figs. 12 and 13. In Fig. 11 I have illustrated a segmental unit, subtending only a part of a circle, only one end of the unit being shown.

The forms of the invention illustrated in Figs. 8 to 13 inclusive are articularly advantageous in cases where suoli a metal clad heating unit lis to be employed with a ceramic plate made of kieselguhr, silocel or othersubstances'having particularly low rates of heat conductivity. In the absence of safety provisions supports of these materials are dangerous to use with metal-clad elements since their heat insulating effect is likely to lead to fusion of the resistor or damage to the metal sheath in case the user fails to place a kettle or other heat absorbing device on the unit.

I do not limit myself to metal-clad elements of any one shape, size, style, construction or material for the features herein set forth are of universal applicability and I desire my claims to be construed broadly, each independent of limitations contained in other claims.

Having thus described myinvention what I claim is:

1. The combination with a metal-clad resistance heating unit of a thermally conducting body adjacent thereto but not in more tlian limited contact therewith, said body bengglargely insulated from said unit at low temperatures and substantially coupled thereto thermally at elevated temperatures.

2. The combination with' a metal-clad resistance heating unit of a thermally conducting body underlying the same, and means be-. tween said unit and bod adapted substantially to insulate them fiifom each other at low temperature differences while connecting them thermally together at high temperature differences.

3. The combination with a metal clad resistance heating unit, of a supporttherefor adapted to embrace and house in a part of sald unit, and means operative when thev difference between the temperatures of said unit and support become of the salne order of magnitude as thev absolute temperature for conveying heat away from the concealed face of said unit.

4. An electric heating device comprising in combination, a supporting member composed of heat conducting material having a supporting face, a metal-sheathed, refractory insulatedl electric resistance element carried thereby and having an outwardly facing working face and an oppositely facing suporting surface which overlies the supporting face of said supporting member in close relation whereby said element is largely insulated from said supporting member at ordinary temperatures, and is thermally connected thereto at elevated temperatures.

5. An electric resistor element, a body of refractory electrically-insulating, heat-conducting material enveloping said resistor, a

sheath of met-a1 embracing and enclosing said body, in combination with a-mass of heat conducting material above which said sheath is supported, said mass and sheath being sufficiently separated to limit heat transfer at low temperatures while permitting free radiation at high temperatures.

6. The combination with a metal-clad, resistance heating element of a body of thermally conducting material closely adjacent to one face thereof and adapted to receive radiant heat therefrom, -said body having a portion opposite the center of the concealed face of said unit and separated from said unit in such wise as not to receive heat by con.- duction to anysubstantial degree.

7. In an electric heating device, in combination, a supporting member having an upwardly opening recess which does not penetrate said member, and a metal-clad, resistybot-tom of said recess having ,ance heating unit located in said recess, the proJections which engage the lower face of said unit and elevate it out of direct contact with the bottom of the groove While permitting free exchange of radiant heat.

8. A metal plate having a de ression in one face thereof and a metal cla resistance heating unit mounted in said depression and seated on the bottom face thereof with its upper face protruding above the top of said plate in vessel receiving position;

9. A metal plate having an upwardly facing, heat, dissipating surface and an upwardly facing depression adjacent thereto, in combination with a metal clad resistance heating EDWIN L. WVIEGAND.

CERTIFlCATE 0F CORRECTIN.

Patent No; 1, 706, 016.

Granted March 19, 1929, to

EDWIN L. WIEGAND.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Page 2, line 57, for the word "magnesis" read "magnesia"; andthat the said Letters Patentshould be read with this correction therein that the same in the Patenty Office.

may conform to the record of the case Signed and sealed this 7th day of May, A. I). 1929.

(Seal) M. J. Moore, Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,706,016. Granted March 19, 1929, to

EDWIN L. WIEGAND.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as fellows: Page 2, line 57, for the word "magnesis" read "magnesia"; and that the said Letters Patent should be read with this correction therein that the seme may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of May, A. D. 1929.

M. J. Moore,

(Seal) Acting Ccmmissioner of Patents. 

